1. Field of the Invention
The present invention relates to a coaxial type starter device. More particularly, it relates to a coaxial type starter device used for starting the engine of an automobile.
2. Discussion of Background
Heretofore, a conventional starter device used for starting the engine of an automobile is of a so called biaxial structure wherein an electromagnetic switch device for feeding power to a d.c. motor is disposed at the side of the d.c. motor.
However, such biaxial type starter device gave a great restriction when an engine for an automobile is to be designed.
There has been a proposal to make the shape of a starter device simple. According to the proposal, the starter device is so constructed that it has a generally elongated cylindrical form by arranging an electromagnetic switch device at an end in the axial direction of a d.c. motor.
The proposed starter device is illustrated in FIG. 3. In FIG. 3, a coaxial type starter device 1 is such that an armature rotary shaft 3 of a d.c. motor 2 is hollow; a plunger rod 4a of an electromagnetic switch device 4 disposed at the rear end of the d.c. motor 2 is extended in the inner passage 3a of the hollow armature rotary shaft 3; and an output rotary shaft 5 is inserted in the armature rotary shaft 3 in a coaxial manner so that the rear end of the output rotary shaft 5 is in contact with the free end of the plunger rod 4a, whereby when the electromagnetic switch device is actuated, the output rotary shaft 5 is pushed forwardly by means of the plunger rod 4a.
A sun gear wheel 6a is formed in the outer circumferential portion of the front end of the armature rotary shaft 3, and a plurality of planet gear wheels 6b are interlocked with the sun gear wheel 6a. The planet gear wheels 6b are also interlocked with an internal gear wheel 6c formed in the inner circumferential surface of a machine frame 7, and each of the planet gear wheels 6b is supported by a carrier 6e by means of each shaft 6d. The sun gear wheel 6a, the planet gear wheels 6b, the internal gear wheel 6c, the shafts 6d and the carrier 6e constitute a planet gear speed-reducing device 6 which reduces a rotating speed of the armature rotary shaft 3.
An overrunning clutch device 8 is fitted to the output rotary shaft 5. A clutch inner member 8a of the overrunning clutch device 8 is interlocked with a helical spline 5b formed in a spline forming section 5a of the output rotary shaft 5, the spline forming section 5a having an outer diameter greater than the inner diameter of the inner passage 3a of the hollow armature rotary shaft 3, whereby the output rotary shaft 5 can receive a rotating force from the clutch inner member 8a and is slidable in its axial direction. A pinion 9 is attached to the front end of the output rotary shaft 5 so as to be engaged with and disengaged from a ring gear of an engine (not shown). When the output rotary shaft 5 is caused to slide forwardly, the pinion 9 is engaged with the ring gear to rotate it.
However, in the coaxial type starter device having the construction described above, when the output rotary shaft 5 is pushed forwardly (in the right in FIG. 3) upon actuating the electromagnetic switch device 4, the output rotary shaft 5 is brought such a state that it is supported in a cantilever form by a bearing metal 10 disposed in the inner passage 3a of the armature rotary shaft 3 at its rear part of the output rotary shaft 5. Accordingly, an abnormally heavy load may be applied to the output rotary shaft 5 at the time of interlocking of the pinion with the ring gear of the engine, whereby the output rotary shaft 5 is deflected. On the other hand, since the clutch inner member 8a of the overrunning clutch device 8 which is interlocked with the output rotary shaft 5 by means of the helical spline is supported at its front end portion by a single bearing 11, the helical spline teeth 5b formed at the outer circumferential portion of the rotary shaft 5 so as to extend in the axial direction, the helical spline teeth 5b having a shorter length, comes in contact with a cut end of the helical spline groove formed in the inner circumferential surface of the clutch inner member 8a in the vicinity of the bearing 11 when the output rotary shaft is pushed forwardly. In this case, there is no supporting member at the rear part and inside the clutch inner member 8a. As a result, the deflection of the output rotary shaft 5 causes the deflection of the clutch inner member 8a, and the axial center line of revolution of the carrier 6a which is formed integrally with the clutch outer member 8b does not become in coincidence with the axial center of the armature rotary shaft 3.
In this case, for instance, when the starter device is rotated at a high speed by receiving a reverse driving force of the engine or when the engine or the starter device is in an idling operation, and if the pinion of the starter device is engaged with the ring gear of the engine by turnning on the key switch of the automobile, this resulting a large shock to the device, the planet gear wheel 6b may be broken or may generate abnormal sounds. It is serious when the bearing metal 10 becomes worn.
In the conventional starter device, the front end portion of the york 2a of the d.c. motor 2 is bent inwardly to form an intermediate bracket 2b. The inner edge portion of the intermediate bracket 2 is further bent inwardly (on the side of the armature), i.e. it is bent along the axial line of the armature rotary shaft to thereby form a bearing supporting portion 2c. A needle bearing 2d is mounted on the bearing supporting portion 2c to thereby support the front end of the armature rotary shaft 3. In FIG. 3, a reference numeral 2e designates magnetic poles in the d.c. motor 2.
However, in the above-mentioned coaxial type starter device, the bearing supporting portion 2c of the intermediate bracket 2b interferes in a magnetic pole fitting jig when a magnetic pole is fitted to the york 2a. Therefore, it was necessary to place the magnetic pole at the rear part in the axial direction with respect to the bearing supporing portion 2c. This necessitates that the entire length of the motor should be large in order to obtain a predetermined torque.